Fabricating a well-designed denture set to replace missing teeth in an edentulous patient is both challenging and time consuming, requiring numerous visits between a patient and a healthcare professional. Moreover, impressions and models are sent back and forth between a healthcare professional and a dental laboratory to achieve a fit and aesthetics satisfactory to dentist and patient, impacting the time required to prepare the final denture.
Traditionally, patient visits are necessary to take impressions of a patient's edentulous ridge, to evaluate the fit of a try-in denture, to check the bite relationship of a try-in denture, and to ensure accurate fit of the final denture. In a first visit, an impression of a patient's oral anatomy is taken which is used by the dental laboratory to form a stone model of the patient's maxillae and mandible, providing information regarding features such as the size and shape of edentulous ridges. Optionally, custom trays may be made from the stone model for taking a final impression in a subsequent patient visit. In a further visit, a patient's bite registration is taken to determine the relationship between mandible and maxillae by inserting wax rims into the oral cavity of a patient. The bite registration information is sent to the dental laboratory for preparation of a try-in denture. The try-in denture is usually composed of a wax denture in which final denture teeth have been hand-set by a laboratory technician.
In further visit, the patient is examined with the wax try-ins for fit and appearance, and the health care professional notes any adjustments that may be required before preparation of the final denture. After all final adjustments are made, a dental laboratory prepares the final denture set based on the wax try-in. As a result of limitations in this process, sometimes the fit of the final denture is inadequate, requiring re-manufacturing of the dentures, repeating all or part of this process.
There is a need to reduce the expense and time required to prepare a final denture set. Savings in time and money can be achieved by reducing the number of visits between the patient and the healthcare professional, and reducing the time it takes the dental laboratory to make a final denture.
It is advantageous to make dentures by methods that reduce the limitations inherent in traditional manufacturing processes. Creating virtual designs by computer-aided design (CAD) methods is effective for reducing the time to make dental restorations. CAD designs complemented by the use of patient data are known for use in dental restorations. Digital patient data may be obtained directly from a patient's mouth by a handheld scanner, or from scan data of negative impressions, from stone models made from the impressions of a patient's mouth. Additionally, input from a virtual library of teeth shapes have been used in conjunction with patient data to create dental restorations. CAD design methods can enhance both the shape and function of the restoration. Optical and contact digitizers used to provide virtual data of a patient's oral anatomy are described in the literature, and some are commercially available.
CAD design used in conjunction with computer-assisted manufacturing (CAM) is known in dental restorations. Automated manufacturing processes include both subtractive and additive processes. Additive processes include those known by terms such as three-dimensional (3D) printing, additive manufacturing, rapid prototyping and rapid manufacturing, and include processes of forming a three-dimensional solid objects from a virtually designed digital model. Additive manufacturing processes, such as 3D printing, are distinct from machining or milling techniques that rely on removal of material by cutting or drilling (a subtractive process).
In 3D printing, a virtual or digital representation of an object is reduced to a physical form by depositing material in a pattern corresponding to a cross-sectional layer of the object. Material which is sufficiently flowable, either as a liquid, or a solid that can be rendered flowable, may be formed layer by layer by a 3D printer. The flowable material is solidified and subsequent layers are formed thereon. Cross-sections of the virtual representation of the object are used to form each layer, for example, by moving a print head over a work piece and activating elements of the print head to create a layer of the object. Printing may be performed by any method known in the art to form layers that ultimately result in a solid object.
Where a liquid is used, a material such as a polymerizable liquid material is printed according to the digital representation. The liquid is hardened in the required pattern, for example by cross-linking, or where a molten thermoplastic material is used, by cooling. Upon sufficient hardening or crosslinking of a first layer, subsequent layers are printed and hardened. The liquid level is raised a short distance and the process is repeated. Each layer corresponds to a cross-section of the virtual representation and a cross-section of the object to be formed. In a further method, the liquid material may be applied as drops in a pattern according to the cross-sectional object to be formed.
In another method, powder is used, instead of liquid, to form the three-dimensional (3D) object. Powder, applied to a substrate in a pattern corresponding to a layer of a digital representation, is hardened by any known method suitable for the selected powder such as heating. Each layer of a 3D object may be created by spreading a thin layer of powder over the surface of a powder bed and hardened or partially hardened as each layer is laid down. Subsequent layers of powder are laid down in sequence upon coalescing of the initial layer to a stable form. Whether liquid or powder, material deposition is controlled by a computing device, such as a computer, personal computer, microcontroller, or the like.
Automated manufacturing processes, used in combination with virtual design process, standardize the manufacturing process and realize both time and cost savings in dental restoration production.